Kayla Major was at work Thursday afternoon just steps from her son’s elementary school in Bend, Oregon, when her co-worker said she heard gunshots and employees started locking the doors.

“I don’t think I even had a first thought,” Major told “CBS Mornings” on Friday. “I think I stood up, they were locking the doors, and I kind of was figuring out what was going on and why they were locking the doors, and then I heard ‘active shooter’ and then I said, ‘Where?’ and they said, ‘the school behind us.'”

“I don’t know if my co-workers understood that I had a child that went to school there, and so I kind of fell back into my seat for a second, and then paced for a minute, and I stood up and I unlocked the doors and I just started running over to the school,” she said.

Major’s son was uninjured, but three students — ages 5, 8 and 11 — and one teacher were killed in the shooting at Silver Rail Elementary School, police said. A 7-year-old child and a 54-year-old teacher were transported to St. Charles Bend Hospital with critical injuries, according to police.

The alleged shooter, a 16-year-old male, was shot and killed by a bystander who entered the school. 

Kayla’s ex-husband, Tyler, said their son didn’t really understand what was going on during the incident.

“I mean, they’re children and, you know, he didn’t even understand that anybody had died until after we picked him up,” Tyler Major said. “So we talked to him about that.”

Tyler Major said he was standing back from the large group of people who had gathered outside the school in the wake of the shooting when he saw another parent be told their child had been shot.

“I just saw an older lady come out and I could tell she was looking for somebody who was going to get some bad news,” he said. “It was heart-wrenching. I had to go take a break and sit down and, I don’t know, grieve for her and for the other families that aren’t going to have their loved ones anymore ever again.”

Police received a 911 call just before 1 p.m. local time from a person who said their truck had been shot several times by a suspect with a long gun. 

The shooter then forced his way into the school by “shooting at locked doors,” Bend Police Chief Mike Krantz said at a press conference Thursday. A motive for the shooting has not been released.